Following the passage of one Action Potential, there is a time delay before the next one can pass. This time delay is known as refractory period and it lasts for a few milliseconds. During this time, the sodium channels in the membrane are closed, preventing the inward movement of Sodium ions. This is known as the absolute refractory period. Another impulse cannot be conducted no matter how large the stimulus is.

Following the passage of one Action Potential, there is a time delay before the next one can pass. This time delay is known as refractory period and it lasts for a few milliseconds. During this time, the sodium channels in the membrane are closed, preventing the inward movement of Sodium ions. This is known as the absolute refractory period. Another impulse cannot be conducted no matter how large the stimulus is.

and..other one m confused bout is....!! When enzymes are immobilized, what will happen?? i mean..they are all covered by those inert materials..or what else?? any if they are all covered..how do they help in a reaction?

Following the passage of one Action Potential, there is a time delay before the next one can pass. This time delay is known as refractory period and it lasts for a few milliseconds. During this time, the sodium channels in the membrane are closed, preventing the inward movement of Sodium ions. This is known as the absolute refractory period. Another impulse cannot be conducted no matter how large the stimulus is.

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Any other definition?!

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When an action potential has just occurred at a section of the axon, there is a short period of time when a second action potential can be generated at the same point. This is called the refractory period.

and..other one m confused bout is....!! When enzymes are immobilized, what will happen?? i mean..they are all covered by those inert materials..or what else?? any if they are all covered..how do they help in a reaction?

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Immobilized enzymes can be recovered easily from a reaction and be used over and over again. The reactant products are not contaminated by the enzyme because the enzyme are held in matrix.

I'm giving a bit of info, it'd be good if anybody could help me with the rest! :unknown:

1) Synapses ensure one-way transmission, as the synaptic vesicles containing the neurotransmitter substances are only present in the presynaptic neurone, and the receptors for these neurotransmitters are only present in the post synaptic membrane.

2) They are involved in memory and learning. This is due to the formation of new synapses which link the neurones that carry information along particular pathways.

Let me know if there's any mistake in the second point. And I'd like some further points which are listed in the mark scheme as follows. I didn't understand those points, so I am unable to link them!

Below are all the points in the mark scheme
-ensure one-way transmission
-receptor only in post synaptic membrane
-vesicles only in presynaptic neurone
-adaptation due to overuse of synapse
-wide range of responses
-due to inter connection of pathways
-inhibitory synapses affect other synapses
-involved in memory/learning
-due to new synapses being formed
-summation

Below are all the points in the mark scheme
-ensure one-way transmission
-receptor only in post synaptic membrane
-vesicles only in presynaptic neurone
-adaptation due to overuse of synapse
-wide range of responses
-due to inter connection of pathways
-inhibitory synapses affect other synapses-involved in memory/learning
-due to new synapses being formed
-summation

Jazak Allah Khair for all the help!

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Your first and second points are correct. The other role of synapse is that it increase the possible range of actions in response to a stimulus. Synapses allow a wider range of behavior than could be generated in a nervous system in which neurones were directly 'wired up' to each other. They do this by allowing the interconnection of many nerve pathways.

This is all I can help for the time being. I am not sure about inhibitory synapses and summation.

whats the role of VASA RECTA.....and ....is vasa recta the name for blood vessels around loop of henle via peritubular cpillaries for around distal and proximal?

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Yup, Vasa recta is the blood capillary which collects the filtered blood from the afferent arteriole. They play an important role in forming concentrated urine. The useful molecules (salts and water) are reabsorbed from renal tubule into the blood in vasa recta. Vasa recta conveys this blood to the renal venules and then these venules unite together to form renal vein.